This invention relates to gate valves, and more particularly, to a gate valve having a rotary opening and closing mechanism.
Many valve mechanisms used in the injection molding industry are constructed in such a way as to divide the flow of plastic as it passes through or around the valve stem. An example of this is found in U.S. Pat. No. 4,268,240, where as the plastic is transferred from the distributing plate to the nozzle, it is divided by the valve stem or rod. Thereafter, the flow is rejoined into a single path with the result that the once divided interfaces form the molded product with undesirable weld lines. These weld lines can adversely affect both the optical and performance qualities of the final molded product and it is significantly advantageous to avoid their creation when molding certain products.
U.S. Pat. No. 4,412,807 shows an apparatus in which the plastic flow channel in the nozzle is kept separate from the valve pin in an effort to avoid dividing the melt stream. The channel is of a crescent shaped cross section which is known to be less than ideal for encouraging plastic flow, especially in the opposing sharp corners. Also, when the valve pin is in the open position to let plastic material to pass into the mold cavity, it creates a stagnant area of poor plastic flow directly adjacent the front face of the pin. These areas of poor plastic flow can result in material degradation which can adversely affect the performance and physical properties of the molded product.
U.S. Pat. No. 4,925,384 shows a similar design which permits the plastic to come into contact with the valve stem but restricts it from passing around the stem to form a weld line. This design also suffers from a melt channel with sluggish flow areas and requires difficult and expensive machining processes to produce the nozzle housing, having an unusual melt channel cross section.
U.S. Pat. No. 5,104,307 shows a ball-shaped closing element at the front of a nozzle with a melt channel portion extending through it. When the ball is turned, it blocks the flow of plastic to the mold cavity. This design requires a bulky, space consuming actuation device which is not suitable for multi-cavity molding where space is restricted and requires a compact actuation means. The ball-shaped element and receptive concave portions of the nozzle are also difficult to manufacture in a manner in which plastic will not leak between them. Additionally, the ball may need to be heated due to the fact that it is attached to and driven by a component external to the heated plastic melt channel system. As such, more complexity is introduced to the overall system.
U.S. Pat. No. 3,873,656 shows a valve having taps which rotate to open or close. This is similar to the approach described above. It is not compact or easy to manufacture and has sharp edges, susceptible to damage, where it mates with the sprue channels. Also, it does not lend itself to multi-cavity molding, as the actuating mechanism would consume space better used for more molding cavities.
A rotating nozzle is shown in U.K. Patent 872,101. The entire injection unit nozzle rotates on an axis parallel to the flow of plastic as opposed to the perpendicular or angular rotation axis of the two patents mentioned previously. The nozzle front portion remains in forced contact with the delivery bushing, to prevent plastic leakage between the two. The construction shown is very bulky, consuming a substantial amount of space. The rotational drive means (not shown or described) is assumed to also require a considerable space for installation. Additionally, the mode of providing the sealing pressure against plastic leak between the nozzle and bushing is the difference in projected areas at the rear of the nozzle versus the front of the nozzle. The area of the back of the nozzle exposed to plastic is large and is expected to provide substantially enough force to keep the nozzle in positive sealing contact with the bushing. This construction is not found to be reliable or dependable as imperfections in the mating surfaces of the nozzle and bushing or debris, which precludes uniform contact between the two, will increase the projected area of pressure at the front of the nozzle and negate the sealing force.
There exists, therefore, a need for a simply constructed rotary actuated gate valve having a space efficient rotary actuated design.